It is known that a technique to extend the light-sensitive wavelength region of silver halide photographic emulsions to a longer wavelength side by adding certain cyanine dyes, i.e., spectral sensitization, is applied as one of the techniques for the production of photographic light-sensitivite materials. It is also known that the sensitivity obtained by this spectral sensitization, i.e., spectral sensitivity, is affected by the chemical structure of sensitizing dyes, and the properties of the emulsions used such as with respect to the halogen composition, crystal habit and crystal system of silver halide, a silver ion concentration, and a hydrogen ion concentration. The spectral sensitivity is further influenced by photographic additives such as stabilizers, antifoggants, coating aids, precipitating agents, color couplers, and hardening agents.
In general, a sensitizing dye is used for sensitization of a given spectral wavelength of light-sensitive materials. It is known that in some cases when this sensitizing dye is used in combination with another specifically selected dye or organic substance, the efficiency of spectral sensitization can be markedly increased. This is called super sensitization. This super sensitization can be said to be a unique phenomenon since, in general, addition of such secondary dyes or organic substances does not often result in an increase of the sensitivity, or rather even lowers the sensitivity. Secondary sensitizing dyes or organic substances which can be used for this super sensitization are very specific. For example, an apparently small difference in chemical structure may exert considerable influence on the super sensitization action. Thus it is very difficult or impossible to predict suitable combinations of dyes for super sensitization based on their chemical structures.
Sensitizing dyes as used in silver halide photographic emulsions for super sensitization should very desirably satisfy several requirements.
One of the requirements is to provide a high spectral sensitivity. It is desired for them to strongly sensitize a specific narrow wavelength region. In particular, in spectral sensitization of the green-sensitive region, it is necessary to increase the sensitivity within a narrow wavelength region. The reason for this is that in the spectral sensitization of the green-sensitive region, if the spectral sensitivity is extended to a longer wavelength region or a shorter wavelength region, overlapping of the green-sensitive region and the red-sensitive region or blue-sensitive region is increased: in color light-sensitive materials, such overlapping increases color turbidity, and, in some cases, increases the sensitivity to safe light, making it difficult to handle such light-sensitive materials.
For this reason, sensitizing dyes providing spectral sensitivity called "J-bands" are usually used. It is desired for the green-sensitivity to be increased without extending the wavelength region of the spectral sensitivity, or preferably while narrowing it.
Another requirement is to cause no undesirable interaction with color couplers and other photographic additives, and further to maintain stable photographic characteristics during the storage of light-sensitive materials.
Another requirement is not to leave any residual color resulting from the sensitizing dyes in the light-sensitive materials after the processing thereof. The elimination of such residual color is required particularly in the rapid processing in which the processing is performed in short periods of time, usually from several to several tens of seconds.
Another requirement is that fog resulting from the sensitizing dyes should be low.
Dye combinations exhibiting super sensitization particularly in the green-sensitive region are described, for example, in U.S. Pat. Nos. 3,580,724, 3,729,319, and 3,397,060. These conventional dye combinations, however, fail to provide light-sensitive materials which are of high green sensitivity, and simultaneously in which the fog is low, the storage stability is good, and the residual color after the processing is sufficiently low.